The invention relates to reflector lamps of the type having a reflector defining an optical axis, a light-source disposed within said reflector and substantially surrounded thereby, and a lens adjacent said reflector having an annular portion which includes a pattern of elongate beam forming elements.
Such a lamp is known from U.S. Pat. No. 4,506,316 (Thiry et al) which discloses a reflector lamp of the PAR (Parabolic Aluminized Reflector) type. PAR lamps are well known in the prior art and have been used extensively for general spot and flood lighting applications. As shown in Thiry, they typically have a reflector body having a parabolic front, or forward, section, a middle reflective section of substantially spherical shape having its focus at the focus of the parabolic section, and a rear section also of substantially spherical shape. A light source, such as an incandescent filament, halogen capsule, or high intensity discharge (HID) arc tube, is focally arranged with its principle axis either aligned with or perpendicular to the optical axis. A lens is sealed to the reflector body, providing a sealed weatherproof unit. PAR lens's typically include stippling, a pattern of lenticules, and/or elongate beam forming elements, such as flutes, to manipulate the light beam emanating from the reflector. The reflector and lens are typically of hard glass and include a medium screw-type or side prong base at the rear of the reflector for connecting the light source to a source of electric power.
In the Thiry PAR lamp, the light source is aligned with the optical axis. The lens has a circular central stippled portion bounded by an annular portion having a plurality of flutes extending substantially radially outward from the stippled portion. In one Thiry embodiment, the flute side edges are straight and extend radially from the optical axis, providing a tapered flute. Thiry also discloses embodiments having pairs of non-tapered flutes with parallel straight side edges. Each flute pair has a common straight side edge which extends radially from the focal axis.
U.S. Pat. No. 4.651.261 (Szekacs) and U.S. Pat. No. 4.473,872 (Puckett et al) disclose PAR lamps with the light source arranged perpendicular to the optical axis. Szekacs' lens has a central stippled portion with a regular pattern of lenticules and oblong beam forming elements parallel to the light source while Puckett's lens has a plurality of concentric fluted rings and an outer annular stippled portion.
It has been found advantageous to arrange the light source coaxial with the optical axis of the reflector. However, in doing so, it is often necessary for a rigid current conductor to axially extend the length of the light source to connect with its end remote from the lamp base. In any lamp having a parabolic reflector, such a conductive support parallel to the light source will create an objectionable shadow in the light beam projected from the reflector. The greater the diameter of the support with respect to the light source, the larger the shadow. Also, the closer the support to the light source, the larger the shadow. In some lamp designs with axial filaments, it becomes necessary to use supports with a diameter greater than the filament diameter and spaced very close to the filament.
Lens designs for parabolic reflector lamps are created to provide uniform distribution of light. Typically, lens prescriptions provide a certain range of maximum intensity of light within a certain angular range of beam spread. For example, a maximum intensity of 13,000-15,000 candela and a beam spread of 10-12 degrees at 50% of this maximum value. In lamps having a conductive support extending axially along the light source, prior art lens designs have not been satisfactory in reducing the shadow in the light beam caused by the axial support.
Accordingly, it is an object of the invention to reduce shadowing in the light beam caused by light source supports disposed between the light source and the reflector.